Obesity hypoventilation syndrome (OHS) is a combination of obesity (body mass index >= 30 kg/m2), daytime hypercapnia (arterial carbon dioxide tension >= 45 mmHg) and sleep-disordered breathing. Statistical data reveals that 10% of the adult population with a body mass index of 30-40 kgm2 develop hypoventilation during sleep. The morbid obese population shows 30-40%. Chronic hypercapnia debases concentration, and efficiency and provokes daytime somnolence. Devolution of cognitive functions eventually can be a source of somatic and mental deterioration. The newest investigations assume, that leptin resistance plays a huge part in the development of chronic hypoventilation. Obesity hypoventilation syndrome of children is a new field to discover in more detail. We aim to identify the group of children - by measuring their respiratory stage and sleeping conditions - who form a higher risk group for respiratory failure and sleep-disordered breathing related to obesity. Between September 2012 and July 2022, 45 children (22 boys, 23 girls; BMI 21-42kg/m2) were enrolled from Semmelweis University Department of Paediatrics. Quality of life questionnaires were used to identify children with low sleep quality and/or attention deficiency. Respiratory function was tested with forced oscillation technique also in lying and sitting position. The group of children with a higher risk of breathing disorder performed polysomnography, and among them, 3 received home noninvasive ventilation therapy after diagnosis. Moreover, 9 children waiting for a polysomnography examination. Enrollment is ongoing. Based on our results, airway resistance augmented during lying position except in one case, without correlation with BMI, and showed wide variability. Respiratory function and quality of life measurement are indicators of a higher risk of sleep-disordered breathing in children, which play a key role also in detection and prevention. K ulcsszavak: gyermekkori elhízás, obezitás hipoventilációs szindróma, noninvazív lélegeztetés gyermekekben